Hemoglobin exists in two allosteric forms. The T (taught) and the R (relaxed) form. These forms have different chemical and physical properties and the relative amounts of R and T hemoglobin can be determined by art recognized techniques such as ultaviolet, infrared, visible, nuclear magnetic resonance, and electron spin resonance spectroscopy. For example, Perutz et al., Biochem., No. 17, 3641 (1978) describes absorption spectra of hemoglobin derivatives, i.e., R.fwdarw.T transition as a function of ligand and inositol hexaphosphate binding. Circular dichroism and chemical reactivity are among other techniques for distinguishing R and T states of hemoglobin. The relative amount of R and T states can be determined by both end-point and kinetic techniques.
Elevated levels of glycosylated hemoglobin are known to be associated with diabetes mellitus. Glycosylated hemoglobin is present in non-diabetics at a level of about 5% of total hemoglobin, while diabetics have 2-4 times that amount (Science, 200, Apr. 7, 1978). Glycosylated hemoglobin level provides an index of a patient's average blood glucose concentration over a long period of time. This index is not affected by short-term fluctuations in blood sugar (hour-to-hour) and, hence, gives a relatively precise reflection of the state of blood glucose control in diabetics.
Glycosylated hemoglobin is commonly referred to as HbA or fast hemoglobin because it migrates faster on a chromatograph column and, indeed, is generally measured by chromatography or electrophoresis.
It has been discovered that the percent of glycosylated hemoglobin in blood can be measured by monitoring the shift in the equilibrium populations of R and T allosteric forms of hemoglobins when the non-glycosylated hemoglobin is reacted with an allosteric site binding substance. This reaction causes a shift from the R to the T allosteric form in the non-glycosylated fraction portion of the hemoglobin. The glycosylated hemoglobin in the blood sample does not contribute to the shift in the equilibrium of the allosteric forms since glycosylation blocks the allosteric binding site. Thus, the higher the percentage of glycosylated hemoglobin in the blood sample, the smaller the shift between allosteric forms upon reacting the hemoglobins with an allosteric site binding substance. The present invention takes advantage of the reactivity of the allosteric binding site which is accessible in non-glycosylated hemoglobin and the resulting shift in the equilibrium of allosteric forms of the glycosylate and non-glycosylated hemoglobin mixture resulting when an allosteric binding site substance is reacted with the non-glycosylated hemoglobin fraction.